System and method for extending depth of field for 2d vision system cameras in presence of moving objects

Abstract

To provide a system for enhanced depth of field (DOF) advantageously used in the form of logistics applications for scanning feature elements and ID codes on objects.SOLUTION: The system effectively combines a vision system, a glass lens designed for on-axis and Scheimpflug configurations, a variable lens, and a mechanical system to adapt the lens to the different configurations without detaching the optics. The optics can be steerable allowing adjustment between variable angles so as to optimize the viewing angle to optimize DOF for an object in the Scheimpflug configuration. One or more of images can be acquired from the object at one angle setting or differing angle settings, with the entire region of interest clearly imaged. In another implementation, the optical path can include a steerable mirror and a folding mirror overlying the region of interest, which allows different multiple images to be acquired at different locations on the object.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to cameras in machine vision systems, and more particularly to cameras having self-adjusting optics for use in locating and decoding (for example) ID codes on objects. [Background technology]

[0002] Vision systems are used in a wide range of applications and industries to measure, inspect, align, and / or decode symbology in the form of machine-readable symbols (such as 2D matrix symbols, also referred to as "IDs"). These systems are based on the use of image sensors to capture images (typically one-, two-, or three-dimensional grayscale or color) of the target or object, and process these captured images using a built-in or interconnected vision system processor. The processor typically includes both processing hardware and persistent computer-readable program instructions that execute one or more vision system processes to generate a desired output based on the processed information of the image. This image information is typically provided in an array of image pixels, each having a different color and / or brightness. In the example of an ID reader (also referred to herein as a "camera"), a user or an automated process captures an image of an object believed to contain one or more barcodes. The image is processed to identify features of the barcodes, and is then decoded by a decoding process and / or processor to obtain the unique alphanumeric data represented by the code.

[0003] In operation, an ID reading device generally serves to illuminate a scene containing one or more IDs. The illuminated scene is then captured by an image sensor in an imaging system via an optical system. The sensor pixels of the array are exposed to light, and the electronic value(s) generated for each pixel by the exposure are stored in an array of memory cells and may be called an "image" of the scene. In the context of an ID reading application, the scene includes an object of interest having one or more IDs of appropriate dimensions and types. The ID(s) are part of the stored image.

[0004] A common use of ID reading devices is to track and segment objects moving along a line (e.g., a conveyor) in manufacturing and logistics operations. An ID reading device, or more typically, multiple reading devices (a collection of reading devices), can be placed on the line at an appropriate viewing angle(s) to capture any expected IDs on the surface(s) of an individual object as each of the surface(s) passes through the field of view. In general, the focal length of the ID reading device relative to the object can vary depending on the placement of the reading device relative to the line and the size of the object.

[0005] A typical ID reader operates to capture a 2D image of an object that may include multiple sides, where the ID code is printed on the object at different heights and / or positional relationships (box faces). It may be difficult for an image sensor to focus on the full working range of an object (typically moving) on ​​which the ID code may be located, especially when the optical axis of the camera assembly is oriented at an oblique (non-perpendicular) angle with respect to one or more faces of the object. To ensure that the working range is properly focused, the depth of field (DOF) of the camera optics should be maximized. In a particular logistics example, it is desirable to be able to accurately image the faces of objects (boxes) that define a height of about 800 mm and a minimum distance between boxes of 200 mm on a conveyor traveling at a speed of up to about 3 m / s (for example).

[0006] Summary of the Invention The present invention overcomes the shortcomings of the prior art by providing a system and method that can be advantageously used in logistics applications (for example) scanning features and ID codes on objects (boxes), as well as other vision system tasks requiring improved DOF. The system and method herein allows the largest size box to be placed at the focal point to minimize the number of cameras and system complexity imaging the same size box. To improve (enhance) the DOF, the system and method effectively combines a vision system, a glass lens designed for normal (on-axis) and Scheimpflug (or other suitable) configurations, a variable (e.g., liquid) lens, and a mechanical system to adapt the lens to different configurations without unscrewing (or otherwise disassembling) the optics and associated mechanisms. In an exemplary implementation, the optics can be steerable, thereby allowing it to be adjusted between variable angles to optimize the viewing angle to optimize the DOF for an object in (for example) the Scheimpflug configuration. One or more images can be taken of the object at one or different angle settings such that the entire area of ​​interest is clearly and accurately imaged. In another exemplary implementation, the optical path can include a steerable (single or two axis) mirror and a folding mirror (optionally) that covers the area of ​​interest. The steerable mirror allows different locations on the box to be scanned and multiple images to be taken, with each image providing a clear image of at least a portion of the entire area of ​​interest.

[0007] In an exemplary embodiment, a system and method may be provided for maximizing depth of field (DOF) for an object imaged by a camera of a vision system. An image sensor may communicate image data to a processor of the vision system. The image sensor may also define an optical axis of the system. A lens assembly may be configured to provide high DOF and low drift, and the lens assembly may define an optical axis of the lens. A variable lens may be arranged between the lens assembly and the image sensor and may change focus in response to the processor. A tilt mechanism may be configured to change the optical axis of the lens relative to the optical axis of the system in response to focus information of the processor to maximize the DOF. The tilt mechanism is constructed and configured to (a) change the relative angle of the lens assembly or (b) change the relative angle of a steerable mirror located between the lens assembly and the object. A folding mirror may be located between the steerable mirror and the object. The tilt mechanism may operate in each of two orthogonal axes. The variable lens may comprise a liquid lens (e.g., a thin film-based liquid lens). The lens assembly may consist of a stack of solid or glass lenses mounted on a tilt mount relative to a housing containing the image sensor, and / or a liquid lens may be mounted on a tilt mount. The lens assembly, variable lens, and image sensor may define an optical path for the object. The optical path may be variable between (a) on-axis and (b) another (off-axis) configuration, in which the optical axis plane of the lens assembly is not parallel to the optical axis plane for the image sensor. The configuration may include a Scheimpflug configuration, or any other acceptable configuration that improves the DOF and / or another desired imaging characteristic. In general, the processor may be configured to locate and decode one-dimensional and two-dimensional ID codes in an image. By way of illustration, an object may pass through the field of view (FOV) of a camera of a vision system in a logistics operation.

[0008] In an exemplary embodiment, a system and method may be provided for maximizing depth of field (DOF) for an object imaged by a camera of a vision system by projecting light from the object along an optical path onto an image sensor through a lens assembly consisting of a solid or glass lens and a variable lens responsive to an image processor. In such a system and method, the optical path may be moved to a prevailing angle by a mechanical system that changes the optical path. The system and method may determine a distance between an object and an image plane of the camera of the vision system based on constraints that may include (a) a speed at which the object moves, (b) a maximum size of the object, and / or (c) a minimum distance between the object and another adjacent object moving at the speed of movement. The prevailing angle of the optical path may be determined relative to the image plane. The variable lens may be set to focus the projected light onto a plane of interest on the object. An image may then be captured with the camera of the vision system. As an example, the mechanical system can change the angle of the optical path by tilting the lens assembly relative to the housing, and / or the mechanical system can change the angle of a steerable mirror located between the lens assembly and the object. A desired DOF can be set by tilting the optical path and adjusting the focus of the variable lens. As an example, the variable lens can be a liquid lens. The exemplary systems and methods can be operative to locate and decode at least one one-dimensional or two-dimensional ID code on the object and / or to target the object passing through a field of view (FOV) of a camera of the vision system. The systems and methods can further be operative to target another object adjacent to the object passing through the FOV and obtain respective images of the object and the other object. The lens assembly, variable lens, and image sensor of the systems and methods can define an optical path for the object. Thus, the optical path can be variable between (a) an on-axis optical path and (b) another (off-axis) configuration, in which the optical axis plane of the lens assembly is not parallel to the image plane.The off-axis configuration may include a Scheimpflug configuration or other suitable configuration to improve DOF and / or other imaging characteristics. Additionally, the systems and methods may operate with a processor in the vision system to locate and decode one-dimensional and two-dimensional ID codes in the images.

[0009] The following description of the invention refers to the accompanying drawings. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 illustrates a vision system for use, for example, in logistics operations, where a camera assembly captures images of the side of an exemplary object (a box) having multiple ID codes disposed at varying heights along the side, with an extended depth of field (DOF) optical configuration enabling improved capture of image data associated therewith.

[0011] [Diagram 2] FIG. 1 is a side cross-sectional view of a generalized camera assembly including an optical system package and an image sensor having a variable tilt mechanism for use with a front glass lens assembly of an optical system in accordance with an exemplary embodiment.

[0012] [Diagram 3] FIG. 1 illustrates the operation of the Scheimpflug principle (for example) for imaging the side of an exemplary object (a box) using a variable tilt mechanism to acquire multiple images of the side at a desired DOF, in accordance with an exemplary embodiment.

[0013] [Figure 4] 1 is a side cross-sectional view of an exemplary variable angle tilt lens assembly and actuator for use with a camera assembly of a vision system, according to an exemplary embodiment.

[0014] [Diagram 5]FIG. 13 illustrates a fixed lens assembly and a steerable (tilt) mirror that directs the light path in a sweeping pattern through an overlying fold mirror, according to one embodiment.

[0015] [Figure 6] 6 illustrates the use of the vision system configuration with steerable and folding mirrors of FIG. 5 to image the side of an exemplary object (box) in a gap relative to an adjacent box.

[0016] [Figure 7] FIG. 7 is a perspective view relating to the operation of the configuration of FIG. 6.

[0017] [Figure 8] 6 is a diagram of the vision system with steerable and folding mirrors of FIG. 5 showing the light path tilted to the leftmost lateral position in an example operational state.

[0018] [Figure 9] FIG. 6 is a diagram of the vision system with steerable and folding mirrors of FIG. 5 showing the light path in a central position, according to an example of an operational state.

[0019] [Figure 10] 6 is a diagram of the vision system with steerable and folding mirrors of FIG. 5 showing the light path tilted to the rightmost lateral position in an example operational state.

[0020] [Figure 11] FIG. 9 shows an example of the operational state of FIG. 8 with a light path intersecting the side of the example box along the leftmost position.

[0021] [Figure 12] 10 shows an example of the operational state of FIG. 9 with the light path intersecting the side of the exemplary box at a central position.

[0022] [Figure 13]FIG. 11 shows an example of the operational state of FIG. 10 with a light path intersecting the side of the example box along the right-most position.

[0023] [Figure 14] FIG. 1 is a diagram of an image of a stack of objects having exemplary ID codes printed thereon, obtained using principles of the systems and methods herein.

[0024] [Figure 15] 1 is a diagram of an image showing an object within an FOV, defining an extended DOF, acquired using the principles of the systems and methods herein.

[0025] [Figure 16] 16A-16C are comparative images of the same object and FOV of FIG. 15, defining a limited area of ​​focused detail using a conventional optical configuration.

[0026] Detailed Description I. System Overview

[0027] FIG. 1 illustrates a vision system configuration 100 for use in providing an improved depth of field (DOF) useful for imaging fine features, such as ID codes, located over a relatively long distance on the surface of an object being imaged. The configuration 100 includes an imaging system (also referred to herein as a "camera assembly") 110 with a corresponding optics package 112 that directs received light from the surface of an exemplary object (box) 120 being imaged onto the surface of a sensor S (described below in FIG. 2). As illustrated, the camera assembly is oriented to capture an image of a side 122 of the box 120, where it is desirable to capture and decode various ID codes 124, 126, and 128 along the height HB of the box. The height variations combined with the small and fine details present in the ID codes can make the task of decoding somewhat difficult. That is, a camera with a conventional DOF can only adequately focus on one or two ID codes, but not all three codes. Acquiring two or more images with varying focus on a single scene can allow ID codes at different distances to be acquired, however this approach can be disadvantageous when objects are moving down a conveyor line (e.g., in a logistics situation), requiring rapid imaging at the inspection location.

[0028] Thus, the exemplary camera assembly 110 as described further below incorporates an angle-adjustable optics package 112 that can change angular orientation during imaging to enable increased DOF. The image sensor (S in FIG. 2) of the camera assembly 110 is typically a 2D grayscale or color pixel array, but can be a 1D array in various embodiments, and is interconnected with a vision system processing (processor) 140. Image data 130 is communicated from the camera assembly 110 to the processing (processor) 140. The processing (processor) 140 can be fully or partially contained within the housing of the vision system camera arrangement 110. The processor 140 performs various vision system processing using the image data communicated from the image sensor. The processing (processor) 140 can include vision tools 142, such as, but not limited to, an edge detector, a segmentation tool, a blob analyzer, a caliper tool, a pattern recognition tool, and other useful modules. The vision system's processing (processor) 140 may also include a conventional or custom configured ID finder and decoder 144 that receives data from the vision system's tools and determines whether ID candidates are present in the image(s) being analyzed. The ID decoder function may then use conventional functional modules as well as custom processors / processing to attempt to decode the ID candidates found in the image.

[0029] Other processing and / or modules can provide various control functions (e.g., autofocus, lighting, image capture triggering, etc.). Such functions will be apparent to one of ordinary skill in the art. In particular, an angle or tilt control processing (processor) 146 is provided. As described below, this function serves to change the tilt of a glass portion (or another optical component such as a mirror, prism, etc.) of the optical system 112 to enable increased DOF according to an exemplary embodiment. Appropriate control data / signals 148 can be communicated from the processing (processor) module 146 to a drive mechanism (described below) for the optical system 112. Additionally, a focus control processing (processor) 147 can provide focus information as part of the control signal information 148 to a variable (e.g., liquid) lens in the optical system 112 of the camera assembly as described further below.

[0030] Alternatively, some or all of the vision system processing (processor) 140 can be contained within a general-purpose computing device 150 such as a PC, server, laptop, tablet or mobile device (e.g., smartphone), which can include a display and / or touch screen 152, and / or other forms of conventional or custom user interfaces such as a keyboard 154, mouse 156, etc. It will be apparent that in alternative embodiments, various processor configurations and implementations can be used to provide the vision system functionality to the configuration 100. Similarly, if the camera configuration is used for tasks other than ID decoding, appropriate vision system processing modules can be utilized. For example, if the vision system is used for inspection, a learning processing module and learning pattern data can be provided.

[0031] Computing device 150 and / or process (processor) 140 are shown linked to one or more data utilization processes and / or devices 160. Results 164 from ID decoding and / or other vision system tasks are communicated to such downstream components and used to perform (for example) logistical operations (e.g., sorting, routing, rejecting packages, etc.).

[0032] By way of non-limiting example, it should be noted that a photodetector or other presence detection device 180 can be placed at an appropriate location along the object stream (e.g., a conveyor line) to emit a trigger signal 182 that is used by the vision system's processor 140 to initiate image capture of the object 120. The detector can also signal when an object has left the inspection zone and await the arrival of a new object to initiate a new series of image captures.

[0033] 2, an exemplary implementation of the camera assembly 110 is shown in further detail. The illustrated camera assembly defines a housing 210 having a number of circuit components (substrates, chips, etc.) 214, 216, 218, including a main board 212 with an image sensor S as described above. The sensor S defines an image plane 220 onto which a focused image of the object 120 is projected by the optical system 112 and converted into pixel data for processing by the vision system. The sensor S defines a system optical axis OAS that extends perpendicularly from the sensor's image plane 220. The optical system defines an image plane 240 that is oriented at a non-perpendicular angle AOP to the system optical axis OAS, and an associated optical system optical axis OAO is disposed at an acute angle (non-parallel angle) AOA to the system optical axis OAS. This angle AOA can be changed based in part on an adjustment mechanism 250 that changes the tilt of at least a portion of the optical system assembly 112. In a non-limiting example, the angle AOA is between about 5° and about 20°. In this exemplary embodiment, the variable tilt part of the optical system 112 is a so-called glass lens 260 at the front of the overall optical system assembly 112. As shown, the glass lens 260, which may be removable, consists of a number of (for example) convex and concave lenses 262, 264 and 266 configured according to known optical principles to achieve a given focal length, etc. Behind the variable tilt (curved double arrow 262) glass lens 260 is a variable focus lens assembly 270. This variable focus lens assembly 270 may be electronically controlled based on a control signal 148 from the processor 140. The variable component may be a mechanical lens or a liquid lens, such as those available from Optotune of Switzerland and Varioptic of France. In such a configuration, liquid lens 270 may be controlled using any suitable focus data (e.g., sharpness detection using a vision tool, including LIDAR, time-of-flight sensors, etc., using an optical parallax rangefinder) to provide input 118 indicating the appropriate focal distance. Such information is processed via focus control processor 147 (FIG. 1) as will be apparent to those skilled in the art.More specifically, the focus of the lens may be controlled by the vision system processor 140 as described above, or by a separate focus processor (or combination of processing components connected to operate in conjunction). The variable lens assembly 270 may be oriented at a fixed angle of tilt and includes a set of rear concave and convex lenses 272, 274, and 276. The overall lens configuration is appropriate to provide the generally desired focal length and DOF for the task. See commonly assigned U.S. patent application Ser. No. 15 / 847,868, filed Dec. 19, 2017, entitled "SYSTEM AND METHOD FOR REDUCTION OF DRIFT IN A VISION SYSTEM VARIABLE LENS," which describes various optical system configurations (e.g., lens stacks) for providing an expanded DOF in the presence of variable lenses, the teachings of which are incorporated herein by reference as useful background information. The optical system 112 may use the illustrated variable focus lens 270 to provide an autofocus function that allows operation within a predetermined focus region.

[0034] The optical system 112, tilted relative to the sensor's image plane 220, generally operates according to the Scheimpflug principle (see also the above-incorporated U.S. Patent Application No. 15 / 847,868 for illustration) with respect to the points on the object surface 130 toward which the optical system axis OAO and the system optical axis OAS are directed. The resulting vision system configuration 100 provides DOF ​​in imaging features with smaller details (e.g., barcodes 124, 126, 128) over a range of distances as shown along the side of the exemplary box 120. That is, the object (box) is entirely focused in the FOV of the camera assembly 110. An illustration of the use of the Scheimpflug principle is shown in diagram 300. In this example, a (e.g.) 3MP image sensor S of the type used herein, having a total diagonal size of (e.g.) 9mm, operates with a (e.g.) 35mm lens L and an aperture setting of F8. The three planes described by the sensor S, the lens L, and the vertical front surface 122 of the object / box 120 (defining the vertical distance V1-V2) intersect at the Scheimpflug point Sc. This particular configuration allows the system to image a box at a height (V1-V2) distance of (for example) 800 mm with a box gap (V2-V3) of 300 mm to the adjacent box 310. It should be noted that the Scheimpflug configuration as described herein is one of various configurations that can be achieved by the (variable) geometry of the lens configurations herein. It is contemplated that other suitable configurations for improving the DOF can be used, including configurations that generally change the optical path between on-axis and another configuration (typically off-axis) in which the optical axis plane of the lens assembly is not parallel to the image plane for the image sensor. The use of such alternative off-axis configurations will be apparent to those skilled in the art of optical configurations.

[0035] The DOF is defined by the intersection between a line defined by the front focus lens plane FF and the front of the box defined by (distance V1-V2). The DOF presents a wedge shape with the apex located at point D. The minimum DOF of interest in this case is given by point (H1-H2), where the DOF for the maximum height of the box is 170 mm. Assuming a frame rate of 20 ms readout time of the camera sensor S, and a movement speed (arrow 320) of the box through the FOV (e.g., using a conveyor) of 4 mm / ms, the number of frames that the camera sensor S can acquire on all sides of the box with acceptable focus is calculated as follows:

number

[0036] II. Steerable Lenses

[0037] Referring to FIG. 4, FIG. 4 shows a variable tilt (steerable) lens assembly 400 that may be integrated with the overall optical system (112) described above. The lens assembly 400 includes a housing 410 that may be attached to the lens mount (e.g., C-mount) of the camera assembly via mating threads or another mounting technique (e.g., set screws, etc.). Alternatively, the housing 410 may be attached to the front of the camera housing via a screw or other fastener using a flange (412). The housing includes a geared motor 420 that receives power and control signals from the angle control processor (146 in FIG. 1) via any suitable motor control circuitry and / or interface. The motor drives a yoke 430 that rotates about the illustrated axis of rotation Sc to generate a non-perpendicular tilt (not parallel to the axis of the sensor system) of the axis OAO of the lens assembly 440 relative to the image plane of the sensor S. The tilt movement is defined by a radius RL between the axis of rotation Sc and a contact point P between the motor 420 and the yoke 430. The axis of rotation Sc can define an orthogonal axis, e.g., perpendicular to and perpendicular to the page as shown (line 426). Thus, the yoke 430 can be configured to move about each of two orthogonal axes under the drive of the motor and / or the second motor 428. The facing surfaces of the yoke 430 and the lens housing 410 can define a two-axis hemisphere that allows free movement, like a ball joint, within a range of tilt angles to each side of the system axes. In this way, the camera can rotate about a given axis regardless of the spatial orientation of the camera housing relative to the object.

[0038] The yoke 430 and motor(s) 420 (and 428) can interact in various ways to achieve an adjustable tilt angle, for example, the yoke 430 can include a gear rack driven by a pinion gear of the motor. The motor can also include a worm drive gear that interacts with a rack attached to the yoke. Alternatively, the motor can drive an elastomeric tire that presses against a smooth or textured contact surface on the yoke. In another configuration, one motor can drive the yoke about the tilt axis, and the entire assembly can rotate about an orthogonal axis, like a gimbal, to provide a second degree of freedom. Appropriate feedback can be sent back to the angle control processor 147 to track the angular position of the lens barrel 440 and its associated axis OAO. Such feedback can be generated by tracking the motor steps (i.e., if the motors 420 (and 428) are configured as stepper motors) or via separate encoders operatively connected in conjunction with the motor and yoke drive trains. In other embodiments, an accelerometer arrangement may be used to track the relative position. Other techniques for tracking the spatial position and positional relationships of the lens assembly 440 may be used. A data / power connection (not shown) between the lens assembly 410 and the housing of the camera assembly may be provided as needed. By way of non-limiting example, this connection may be interengaging contact pads that come into contact when the lens housing 410 is attached to the camera housing, or a detachable cable 450 that runs from the lens housing 410 to a socket (not shown) on the camera housing.

[0039] In addition to powering and controlling the motor 420, the cable 450 described above can connect the variable (e.g., liquid) lens assembly 460 to a focus control (147 in FIG. 1) on the vision system's processor 140. The liquid lens 460 in this example is integrated with the barrel 464 of the overall lens assembly 440 and tilts with the barrel 464. The barrel 464 collectively houses the front glass lens arrangement (stack) 466, the variable / liquid lens 460, and the rear lens arrangement (stack) 468. In an alternative configuration, only the front glass lens arrangement can be tilted, while the liquid lens and / or the rear glass lens arrangement remain stationary relative to the sensor S. In general, the number of glass lenses in the barrel 464 and their arrangement are highly variable based on the desired characteristics of the optical system.

[0040] During operation, the motor 420 operates to tilt the lens assembly 440 in different orientations about the axis Sc while the focus of the liquid lens 460 is adjusted to the appropriate focal length to image each portion of the entire FOV to fully cover the required DOF across the sides of the object. In particular, the focus position of the lens 460 can be adapted to the sensor S for different usage situations (i.e., the focus of a 24 mm lens is different from the focus of a 35 mm lens), and the system allows flexibility to address these physical differences and to provide the user with options in selecting the lens assembly that best suits a given task. More specifically, as the motor 420 tilts the lens, focus feedback causes the processor (147) to adjust to the appropriate focal plane for that tilt setting.

[0041] It should be noted that part of the information provided to the processor may include the current angle of the lens relative to the camera axis. This is used in combination with other information to set the focus of the variable (liquid) lens to place the plane of interest on the object at the proper focus. The system also determines the distance between the object and the camera image plane. This data is combined with other system / application constraints, including the speed of object movement through the FOV, the maximum size of the object, and the minimum distance between objects (discussed further below).

[0042] III. Steerable and Folding Mirrors

[0043] An alternative configuration 500 for providing a variable angle to the lens optical axis (while following the Scheimpflug principle) is shown in FIG. 5. A lens assembly 510 is oriented relative to the sensor S. The lens assembly 510 may include a suitable lens stack including a variable (e.g., liquid) lens, as described above. The variable lens is controlled by the focus control processor 147, described above. A steerable mirror 530, sized to reflect the FOV onto the sensor S, is placed in front of the lens assembly 510 along the optical path 520. The overall configuration defines the Scheimpflug principle described above. The steerable mirror 530 may be pivoted on one or two orthogonal axes (curved double arrows T1 and T2). The optical path 520 extends onto an overlying folding mirror 550, which may be mounted in a convenient location relative to the scene to be imaged (e.g., a conveyor surface 560).

[0044] In operation, the folding mirror 550 is oriented into an appropriate configuration to image the scene, and the steerable mirror 530 tilts (in response to the angle control processor 146) along one or both axes to allow the system to scan different sections of the conveyor while sweeping rapidly across the vertical direction of travel. The steerable mirror 530 can be actuated using a variety of techniques (e.g., servo, stepper, voice coil, etc.), which will be apparent to those skilled in the art. The steerable mirror 530 can be integrated with the optics of the camera assembly so that it is fully enclosed and appropriately protected from the environment (e.g., using a transparent viewing window).

[0045] As shown in Figures 6 and 7, an optical system assembly with a steerable mirror 610 (the combination of lens 510 and mirror 530 of Figure 5) is shown in operation to read an ID code (or other feature) along a side 622 of an exemplary box 620 located adjacent to a second box 630 in the gap space G between the boxes. The scene to be imaged is defined by the positioning of a folding mirror 550 that is positioned and tilted to direct the FOV over the height of the side 622 of the box. The sweeping motion of the steerable mirror can bring various regions of this height (and width) into focus as the box moves (arrow 640) at a predetermined speed along the conveyor line 650. Sufficient frames are acquired from the box during the scanning motion of the optical path 520 to ensure that all features along the side 622 are adequately imaged for decoding. In one example (mentioned above), the boxes have maximum dimensions of about 800mm x about 800mm x about 800mm, although this maximum size (in some or all dimensions) is highly variable in alternative implementations. More specifically, this configuration is well suited for logistics applications. In such applications, the maximum height of the boxes is about 800mm, and the minimum gap distance between the boxes is 200mm. The boxes can pass through the system's FOV at speeds of up to 3m / s. The system desirably allows for the largest anticipated size of the boxes to be placed at the focal point, thereby minimizing the number of cameras, minimizing both the number and complexity of the cameras in the system.

[0046] As further shown in Figures 8-13, the steerable mirror 530 is tilted variously (e.g., left position, center position, right position) such that the optical path 520 is redirected laterally such that the associated FOV can cover the entire horizontal (width) dimension of the side 1122 of the exemplary object (box 1120). This is accomplished with three distinct positions (and image frames) in the illustrated example, although more or fewer lateral positions (e.g., positions between the left and center positions and positions between the right and center positions) may be used in alternative implementations. As illustrated, the optical path 520 is directed laterally approximately 8° to the left by the steerable mirror 530 in Figures 8 and 11 as image frames are acquired, thereby covering the left portion of the side 1122 of the box along approximately its height. In Figures 9 and 12, the central portion of the side 1122 of the box is imaged, with the optical path 520 at approximately 0° (neutral) in place. Then, in Figures 10 and 13, the optical path 520 is steered laterally to the right to image the right portion of the side 1122 of the box. By properly overlapping the three images produced by this scanning process, the entire side is fully imaged with enough detail to find and decode the ID features of the minimum size ID code. It should be noted that the use of a tilt angle of + / - 8° is exemplary, and a wide range of possible angles can be used based on the prevailing FOV and DOF of the system, the size of the features to be imaged, and the size of the total object under inspection.

[0047] IV. Operational Performance

[0048] Advantageously, the exemplary implementation maximizes image quality and focus while widening the DOF. The glass lens components can advantageously operate in both a normal mode, where its optical axis is perpendicular to the sensor plane, and in a Scheimpflug configuration, allowing substantial flexibility that can benefit a variety of vision system tasks, including (for example) logistics applications that require scanning of the top / side of an object. More specifically, the configuration allows for maximized DOF for moving objects viewed from extreme viewpoints. These performance characteristics also allow the number of cameras used to image an array of objects to be minimized. That is, other systems based on multiple cameras generally require a relatively large number of readers to cover the same DOF as the exemplary configurations herein, but such other systems suffer from perspective distortion, reduced usable FOV, and the requirement of different focal lengths for each camera in the system. Generally, the systems in question must incorporate three or four cameras (significantly increasing the system complexity and the amount of data to be processed) to perform the same operations that a single (or possibly two) camera assembly can perform here. The exemplary configuration also incorporates inherently low drift characteristics, allowing for conventional autofocus functionality. It should be noted that the exemplary configuration maximizes DOF ​​with no modifications to the sensor or camera housing hardware, aside from the use of modified optical mechanics in the lens configuration and in front of the lens (e.g., a folding mirror).

[0049] 14, which illustrates the results of an exemplary image of a plurality of objects (stack of boxes) 1410 acquired according to an exemplary embodiment herein. In this example, a camera assembly 1420 having (for example) a 24 mm F6 lens was implemented in a tilted position while operating with a 5-Mp image sensor. The lens position is arranged to focus on a plane of interest 1430 of the object(s). In this configuration, the FOV is increased such that the plane of interest 1430 defines a viewing height of approximately 750 mm. Generally, distortions may be observed inside the plane of interest 1430. The upper image portion 1440 and the lower image portion include relatively small (e.g., 10 mils (0.254 mm) (which is generally a minimum size in various logistics applications)) identifiable ID codes 1442, 1452.

[0050] Similarly, Figure 15 shows an image 1500 of an FOV with a sharply focused region (arrow 1510) spanning substantially the entire height using the principles of the systems and methods herein that provide improved DOF. Conversely, in Figure 16, a smaller focused region (arrow 1610) results in an image 1600 of the same FOV using conventional optics.

[0051] V. Conclusion

[0052] As is apparent, the above-described system and method effectively widens the DOF and effectively widens the ability to accurately image higher objects by advantageously combining a vision system, glass lenses designed for both normal (on-axis) and Scheimpflug configurations, variable (e.g., liquid) lenses, and a mechanical system for adapting the lenses to different configurations without unscrewing (or otherwise dismantling) the optics and associated mechanisms. This system and method effectively addresses specific problems faced in, for example, logistics applications, and provides ID code reading devices with improved features that improve performance, reduce installation complexity, provide more flexibility over a single lens, and can now be utilized in different applications. In particular, the above-described system and method (in various embodiments) does not require the acquisition of multiple images that sweep different optical powers over all or part of the available dynamic range and / or comprehensive calibration before runtime operation.

[0053] The foregoing is a detailed description of exemplary embodiments of the present invention. Various modifications and additions may be made without departing from the spirit and scope of the present invention. Features of each of the various embodiments described above may be combined with features of other described embodiments as necessary to provide a variety of combinations of features in related new embodiments. Moreover, while the foregoing describes a number of separate embodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of the present invention. For example, as used herein, various direction and orientation terms (and grammatical variations thereof), such as "vertical," "horizontal," "up," "down," "lower," "top," "side," "front," "rear," "left," "right," "forward," "rearward," etc., are used only as relative conventions and not as absolute orientations with respect to a fixed coordinate system, such as the direction of gravity. Moreover, the terms "substantially" or "about," when used with respect to a given measurement, value, or characteristic, mean an amount that is within a normal operating range for achieving a desired result, but includes some variation due to inherent imprecision and error within the tolerances of the system (e.g., 1-2%). It should also be noted that, as used herein, the terms "process" and / or "processor" should be broadly construed to include various electronic hardware and / or software-based functions and components. Furthermore, the illustrated "process" or "processor" may be combined with other processes and / or processors, or divided into various sub-processes or sub-processors. Such sub-processes and / or sub-processors may be combined in various ways according to embodiments of the present disclosure. Similarly, any function, process and / or processor herein may be implemented using electronic hardware, software consisting of a non-transitory computer-readable medium of program instructions, or a combination of hardware and software. Thus, this description is intended to be construed as merely illustrative, and is not otherwise intended to limit the scope of the present disclosure.

[0054] In the following, exemplary embodiments of the present invention will be described, which are combinations of various elements. 1. A system for maximizing depth of field (DOF) for an object imaged by a camera of a vision system, comprising: an image sensor for communicating image data to a processor of the vision system and defining an optical axis of the system; a lens assembly configured to provide high DOF and low drift and defining an optical axis of the lens; a variable lens disposed between the lens assembly and the image sensor, the variable lens being responsive to the processor to change focus; a tilt mechanism for varying the optical axis of the lens relative to an optical axis of the system in response to focus information of the processor to maximize DOF. 2. The system described in claim 1, wherein the tilt mechanism is constructed and configured to (a) change the relative angle of the lens assembly, or (b) change the relative angle of a steerable mirror located between the lens assembly and the object. 3. The system of claim 2, wherein a folding mirror is positioned between the steerable mirror and the object. 4. The system of claim 2, wherein the tilt mechanism operates in each of two orthogonal axes. 5. The system described in claim 1, wherein the variable lens comprises a liquid lens. 6. The system described in claim 5, wherein the lens assembly consists of a stack of solid or glass lenses mounted on a tilt mount relative to a housing that contains the image sensor, and the liquid lens is mounted on the tilt mount. 7. The system described in claim 1, wherein the lens assembly, the variable lens, and the image sensor define an optical path for the object, the optical path being variable between on-axis and off-axis configurations, and in the off-axis configuration, the optical axis plane of the lens assembly is not parallel to the optical axis plane for the image sensor. 8. The system described in paragraph 7 above, wherein the off-axis configuration includes a Scheimpflug configuration. 9. The system of claim 1, wherein the processor is configured to locate and decode one-dimensional and two-dimensional ID codes in an image. 10. The system described in claim 9, wherein the object passes through the field of view (FOV) of a camera of the vision system in a logistics operation. 11. A method for maximizing depth of field (DOF) for an object imaged by a camera of a vision system by projecting light from the object along an optical path onto an image sensor through a lens assembly consisting of a solid or glass lens and a variable lens responsive to an image processor, the optical path being moved to a prevailing angle by a mechanical system that varies the optical path, comprising: determining a distance between the object and an image plane of a camera of the vision system based on constraints including at least one of: (a) a speed at which the object moves; (b) a maximum size of the object; and (c) a minimum distance between the object and another adjacent object moving at the speed of movement; determining the prevailing angle of the optical path relative to the image plane; configuring the variable lens to focus projected light onto a plane of interest on the object; and capturing an image with a camera of the vision system. 12. The method of claim 11, wherein the mechanical system changes the angle of the optical path by tilting the lens assembly relative to a housing or by changing the relative angle of a steerable mirror located between the lens assembly and the object. 13. The method of claim 11, further comprising setting a desired DOF by tilting the optical path and adjusting the focus of the variable lens. 14. The method of claim 11, wherein the variable lens is a liquid lens. 15. The method of claim 11, further comprising locating and decoding at least one one-dimensional or two-dimensional ID code on the object. 16. The method of claim 11, further comprising targeting the object as it passes through a field of view (FOV) of a camera of the vision system. 17. The method of claim 16, further comprising targeting another object adjacent to the object passing through the FOV and acquiring respective images of the object and the other object. 18. The method of claim 11, wherein the lens assembly, the variable lens and the image sensor define an optical path for the object, the optical path being variable between an on-axis and an off-axis configuration, and in the off-axis configuration, the optical axis plane of the lens assembly is not parallel to the image plane. 19. The method of claim 18, wherein the off-axis configuration comprises a Scheimpflug configuration. 20. The method of claim 11, further comprising locating and decoding, with a vision system processor, one-dimensional and two-dimensional ID codes within said image.

Claims

1. 1. A system for increasing depth of field (DOF) for an object imaged by a camera of a vision system, comprising: an image sensor for communicating image data to a processor of the vision system and defining an optical axis of the system; a lens assembly comprising a solid or glass lens and defining a steerable lens optical axis; a variable lens disposed between the lens assembly and the image sensor, the variable lens changing focus in response to a control signal from the processor; a tilt mechanism for steering the steerable lens optical axis relative to the system optical axis in response to a control signal from the processor to widen the DOF; The variable lens changes focus based on a current relative angle of the steerable lens optical axis.

2. 2. The system of claim 1, wherein the tilt mechanism is constructed and configured to: (a) change the relative angle of the lens assembly; (b) change the relative angle of the lens assembly and the variable lens; or (c) change the relative angle of a steerable mirror located between the lens assembly and the object.

3. 2. The system of claim 1, wherein the tilt mechanism is constructed and configured to change a relative angle of a steerable mirror located between the lens assembly and the object, and a folding mirror is located between the steerable mirror and the object.

4. The system of any one of claims 1 to 3, wherein the tilt mechanism rotates about each of two orthogonal axes of rotation.

5. The system of claim 1 , wherein the variable lens comprises a liquid lens.

6. The system of claim 1 , wherein the lens assembly, consisting of a solid lens or a glass lens, is mounted on a tilt mount relative to a housing that contains the image sensor, and the variable lens includes a liquid lens mounted on the tilt mount.

7. 2. The system of claim 1, wherein the lens assembly, the variable lens, and the image sensor define an optical path for the object, the optical path being variable between an on-axis configuration and an off-axis configuration, and in the off-axis configuration, an optical axis plane of the lens assembly is not parallel to an image plane for the image sensor.

8. The system of claim 7 , wherein the off-axis configuration comprises a Scheimpflug configuration.

9. The system of any one of claims 1 to 8, wherein the processor is configured to locate and decode one-dimensional and two-dimensional ID codes in images.

10. The system of claim 9 , wherein the object passes through a field of view (FOV) of a camera of the vision system in a logistics operation.

11. 1. A method for increasing depth of field (DOF) for an object imaged by a camera of a vision system by projecting light from the object along an optical path onto an image sensor through a lens assembly consisting of a solid or glass lens and a variable lens that changes focus in response to a control signal from a processor of the vision system, the optical path being moved to a prevailing angle by a mechanical system that steers the optical path, comprising: determining a distance between the object and an image plane of a camera of the vision system based on constraints including at least one of: (a) a speed at which the object moves; (b) a maximum size of the object; and (c) a minimum distance between the object and another adjacent object moving at the speed of movement; determining the prevailing angle of the optical path relative to the image plane; steering the optical path with the mechanical system based on the prevailing angle; setting the variable lens to focus the projected light to a plane of interest on the object based on the determined prevailing angle of the light path; and capturing an image with a camera of the vision system.

12. 12. The method of claim 11 , wherein the mechanical system changes the angle of the optical path by: (a) tilting the lens assembly relative to a housing that contains the image sensor; (b) tilting the lens assembly and the variable lens; or (c) changing the relative angle of a steerable mirror located between the lens assembly and the object.

13. 13. The method of claim 11 or 12, further comprising setting a desired DOF by tilting the optical path and adjusting the focus of the variable lens.

14. The method according to any one of claims 11 to 13, wherein the variable lens is a liquid lens.

15. The method of any one of claims 11 to 14, further comprising locating and decoding at least one one-dimensional or two-dimensional ID code on the object.

16. The method of any one of claims 11 to 15, further comprising targeting the object as it passes through a field of view (FOV) of a camera of the vision system.

17. The method of claim 16 , further comprising targeting another object adjacent to the object passing through the FOV and acquiring respective images of the object and the another object.

18. 12. The method of claim 11 , wherein the lens assembly, the variable lens and the image sensor define an optical path for the object, the optical path being variable between an on-axis configuration and an off-axis configuration, and in the off-axis configuration, an optical axis plane of the lens assembly is not parallel to the image plane.

19. The method of claim 18 , wherein the off-axis configuration comprises a Scheimpflug configuration.

20. 12. The method of claim 11, further comprising locating and decoding, with a processor of the vision system, one-dimensional and two-dimensional ID codes in the image.

Images